The present invention relates to a manufacturing process of an electrical conductor or circuit compensated for radio interferences such as micro-discharges, and an electrical conductor or circuit obtained by this process.
In the field of processing of electrical signals then their storage or their transformation into sensory phenomena directly perceived by human physiological receptors, numerous works have been carried out up to the present in order to maintain, indeed improve, the signal to noise ratio after each transformation, due to the processing, with the object of improving the reproduction and therefore the perception of these sensory phenomena.
Such concern is not moreover specific to the single field of sensory phenomena, such as the reproduction of sounds, but appears also in the much wider field of electronic signals creation, their transmission, their storage and their use by electronic or electrical transducers specially adapted to this purpose.
With regard more particularly to the field of creation, processing, storage and then reproduction of the sound in high fidelity technology, particularly, the HiFi field, some particularly well informed audiophile listeners, noted and reported, from 1970, that they could detect perceptible variations in tone between HiFi systems according to the nature of the power amplifier-loud speaker or acoustic enclosures connection cables.
Some did not hesitate, moreover, to note still more perceptible differences in musical quality, in their opinion, at the time of changing the modulation cables connecting, for example, a source such as a disc player, a microgroove disc or a tuner at the input of the power amplifier, or even of the pre-amplifier.
Quick studies conducted by recognized physicists, demonstrated, rightly, that the resistance in ohms of the most resistive of these wires or connection cables was very inferior to the impedance of loud speakers or acoustic enclosures, all the more so to the input impedance of amplifiers or pre-amplifiers, and that, consequently, such variability displayed above all a subjective character.
A more complete study, based on the theory of electrical lines, allowed taking into account the whole of the localized or distributed characteristics likely to affect the transmission and therefore the reproduction of these signals, i.e. in fact to the whole of the signals generated from a source or radiated in the radio space.
For an amplifier-loud speaker connection, the equivalent diagram can be reduced, as shown in FIG. 1a, to;
a capacitance C between conductors, a function of the geometric size of the cables and the nature of the electrical insulations;
an inductance L divided into two components L/2, corresponding to the magnetic field produced by the current flowing in the conductors;
an internal impedance Zi, for each conductor comprising a resistive part and an inductive part due to the skin effect, on the surface of the conductors, and to a proximity effect of these latter.
As regards the skin effect or Kelvin effect, it is recalled that this phenomenon is characterized by the fact that in alternating current, the current density reduces, with the frequency, at the center of the conductor, and increases at the periphery, as shown in FIG. 1b. 
For this phenomenon, the depth of penetration xcex4 in meters is given by the relation:                     δ        =                              ρ                          π              ⁢                              xe2x80x83                            ⁢                              μ                0                            ⁢                              xe2x80x83                            ⁢              f                                                          (        1        )            
relation in which:
xcfx81 designates the resistivity of the conductor in xcexa9xc3x97m;
xcexc0=4xcfx8010xe2x88x927 designates the vacuum permeability;
f designates the frequency of the transmitted signal in Hz.
Taking account of this phenomenon, because of the reduction of the actual conduction surface of the conductor, it is possible to define a cut-off frequency fc associated with a conductor radius r of specified nature:                     fc        =                                            k              2                        ⁢            ρ                                2            ·            π            ·                          r              2                        ·                          μ              c                                                          (        2        )            
relation in which:
k=1.910852
r designates the conductor radius,
xcfx81 and xcexc0 having been defined previously.
The maximum radius of the conductor for a maximum frequency to transmit fc is given by:                     r        =                  K          ⁢                      xe2x80x83                    ⁢                                    ρ                              2                ⁢                                  xe2x80x83                                ⁢                                  π                  ·                  fc                  ·                                      μ                    0                                                                                                          (        3        )            
Thus, for copper, fc=20 kHz, r=0.623 mm, i.e. xcfx86=2r=1.25 mm is obtained. The depths of penetration are given by:
These results show that this depth varies a great deal as a function of the frequency of the transmitted signal, to be precise in the audiofrequency range. Consequently, it is recommended as far as HiFi technology is concerned to make modulation connections by means of a conductor with a strand diameter less than 6/10 mm, the connection between the amplifier and acoustic enclosures being made by means of strands of 5/10 to 6/10 mm placed in parallel in order to obtain cables with a cross section between 1.5 and 3 mm2, as a function of the length, each strand being individually insulated. The only real effect of any use of cables with a greater cross section is a poorer attenuation of the signals at low frequencies and therefore a relative xe2x80x9craisingxe2x80x9d effect of these latter.
Besides the aforesaid phenomena, in particular as far as the amplifier-acoustic enclosure connection cables are concerned, these latter can be subjected, as shown in FIG. 1c, to a proximity effect. This effect only appears during transmission of periodic or pseudo-periodic signals, at high frequencies, the currents flowing in the parallel return conductors having the effect of minimizing the emitted magnetic flux. An approximate calculation enables an impedance coefficient value of the transmission cables to be established at high frequencies, greater than 10 kHz in the audio-frequency field, taking account of both the skin effect and the proximity effect, for two parallel conductors of circular cross section of diameter xcfx86 and the central axes of which are distant by D. This impedance coefficient, expressed in xcexa9/m, establishes the relation:                     Zi        =                  ρ                      Pm            xc3x97                          xe2x80x83                        ⁢            δ            ⁢                          xe2x80x83                        ⁢                          (                              1                -                                                      k                    2                                    ⁢                                      xe2x80x83                                    ⁢                                                            φ                      2                                                              D                      2                                                                                  )                                                          (        4        )            
In this relation, K, xcfx81 and xcex4 are the parameters defined previously in the context of the skin effect phenomenon, Pm represents the perimeter of each conductor. The product Pmxc3x97xcex4 represents the useful cross section presented to the current and the term   (      1    -                  K        2            ⁢              xe2x80x83            ⁢                        φ          2                          D          2                      )
represents the proximity effect contribution. This contribution is however negligible as soon as D greater than  greater than xcfx86.
The previous relation (4) is essential, for it enables it to be established, contrary to unconvincing conclusions or practices, that conductors having a same ohmic resistance and a same xcfx86/D ratio have an absolutely identical behavior according to the transmitted signal frequency. Consequently, the choice of the nature of the constituent metal of the conductors, copper, gold, silver, aluminum, provided that the ohmic resistance and the xcfx86/D ratio characteristics are satisfactory, is not able to have any influence on the cable behavior as a function of the transmitted signal frequency.
The theory of lines applied to the acoustic enclosure cables, each cable component being modeled by a transfer function xcex93 of characteristic impedance Zc=v(Z/Y), where Z represents the series impedance of the conductor, with Z=Zi+jLxcfx89, j={square root over (xe2x88x921)} and xcfx89=2xcfx80f, Y=jCxcfx89 parallel admittance, and of propagation constant xcex3={square root over (ZY)} enables the amplifier-acoustic enclosure function to be established, as is shown in FIG. 1d, in the form                                           V            2                                V            1                          =                  l                                    ch              ⁢                              xe2x80x83                            ⁢              γ              ⁢                              xe2x80x83                            ⁢              l                        +                                                            Z                  C                                z                            ⁢                              xe2x80x83                            ⁢              sh              ⁢                              xe2x80x83                            ⁢              γ              ⁢                              xe2x80x83                            ⁢              l                                                          (        5        )            
where z designates the complex impedance of the acoustic enclosure, l designating the length of the line, i.e. of the connection. For frequencies in the audio field and for a connection length l less than 10 meters, ch xcex3lxe2x89xa11 and sh xcex3lxe2x89xa1xcex3l, the relation (5) is simplified to:                                           V            2                                V            1                          =                  l                      l            +                          l              ⁢                              xe2x80x83                            ⁢                              Z                z                                                                        (        6        )            
with Z expressed in xcexa9/m, z in xcexa9, and l in meters. The theory of lines shows therefore that in principle:
any amplifier-acoustic enclosure connection cable is assimilable to its own impedance;
the capacitance of this cable is negligible.
Taking account of the previous analysis, the only phenomenon likely to induce a perceptible variation in the sound quality of HiFi systems, as a function of the nature of the connection cables, can apparently be ascribed to the skin effect alone, or even the proximity effect.
Additional investigations then caused M. JOHANNET to take into account moreover the phenomena usually considered as xe2x80x9caccessoryxe2x80x9d, but nevertheless very real, such as:
the phenomenon of contacts between strands, the case of non insulated multi-strand conductors,
the phenomenon of memory in the insulations of cables, a phenomenon in essence very complex.
The phenomenon of contacts between non insulated strands, as shown in FIG. 1e, causes the appearance of inter-strand current trickles, as well as intra-strand current trickles, the inter strand current trickles being subjected to non linear intra-strand resistances, in particular for low level signals. This phenomenon is accentuated in the presence of oxides at the interface of the strands, which explains the advantage of the use of copper or de-oxygenated materials. The solution consisting in using individually insulated strands, of diameter less than 6/10 mm, in order to combat the skin effect, has been proposed and is currently used. However, this solution introduces a difficulty connected to the very complex aforesaid phenomenon, relative to the phenomenon of memory in the insulations and at the level of the metal-insulation and insulation-air interfaces.
The phenomenon of memory of the insulations is known and has been particularly studied by Jacques CURIE at the end of the 19th century. It can be highlighted following the pulse discharge of an electrical capacitor charged to a starting electrical voltage V, by the more or less rapid return of the voltage, to the capacitor terminals, at a fraction of the starting voltage V. The hypotheses allowing this phenomenon to be explained require, either the complete non release, during the discharge, of the free electrons or ions which have penetrated, during the charge, into the interior of the insulating dielectric material of the capacitor, or an xe2x80x9cinertiaxe2x80x9d of the molecules of the capacitor insulation, the polar axis of which is moved at the time of the charge but does not totally recover its initial position at the time of discharge, or again a combination of these hypotheses.
A proposed solution to reduce this phenomenon has consisted in polarizing the cable insulations by means of an external electrical voltage, applied to the insulation by means of a high resistance. Such solutions, applied to the amplifier-acoustic enclosure connection cable, PTT polarized cable, and to the polarized FLATLINE cable, have seen their level of result accepted in the audiophile circle and constitute a reference within the A.F.D.E.R.S., the French Association for the Development of Recording and Sound Reproduction, 6, rue Myrha, 75018 Paris.
This acceptable and accepted solution has not however allowed the physical nature of this undesirable phenomenon to be established. With regard to the HP PTT polarized cables, the very low resultant capacitance, some 10 pF/m , does not seem to be of the type to cause such a phenomenon. Similarly, for the FLATLINE modulation cable, its width not exceeding 1.2 mm cannot really pose a problem in relation to the skin effect, whereas the insulation used, TEFLON, polytetrafluorethylene, is one of the best electrical insulations, although not perfect.
Besides the aforementioned solutions, an existing solution, that consisting in using an enameled cable, had gained the attention of interested parties. In particular, these cables, used in tube amplifier output transformers have always demonstrated an excellent behavior, without appreciable reaction from well-informed audiophiles. They consist of a copper conductor of some tenths of a millimeter or more, covered with a layer of enamel with a polyurethane varnish base, in one or several layers.
As regards amplifier-loud speaker connection cables of enameled wires, each cable is constituted from two independent separate conductors, each conductor being constituted from 8 to 16 basic strands of 5/10 mm twisted enameled wire, to make a cross section of 1.57 to 3.14 mm2, as a function of the length of the connection. In order to reduce to the maximum the skin and proximity effects, each basic wire is undifferentiated in the twist, and, consequently, occupies successively in the twist all the positions in the overall conductor cross section. The connection of the cable to a connection pin is carried out to professional quality by means of a tin bath at 600xc2x0 C. which volatizes the enamel and tins the copper. A polarization can be made by means of an additional strand or by one of the strands not subjected to the signal to be transmitted.
As regards the modulation cable, the most immediate solution consists simply in connecting core and ground of the connectors by two enameled wires of 5/10 mm. In order to limit the capacitance of the cable, a tight twisting of the two enameled wires can be made, an optimum twisting with pitch close to 1 cm pitch being the only one conceivable. A significant improvement of this type of modulation cable can consist, as shown in FIG. 1f, in inserting a 1/1 transformer at the output of the modulation source and a ferrite core on the cable before the input on the amplifier. These measures allow the very disrupted common mode signals to be definitively blocked, signals passing simultaneously in the two conductors, when these signals stem from sources such as tuners or optical disc (CD) players for example. The aforementioned measures and improvements allow excellent results to be obtained equaling, indeed surpassing, appreciably, those obtained by means of HP PTT and FLATLINE polarized cables.
The physical nature of the improvement thus made, apart from the blocking of the common mode signals, did not always however immediately appear. For this reason, M. JOHANNET was led to pursue again his investigations starting from a particularly simple 2xc3x971 W amplification circuit, the diagram of which is given in FIG. 1g. This amplifier drawing published in the Audiophile journal No.32, in France, March 1995, concerns an amplifier with integrated circuit and transistors, conceived originally so as to attenuate thermal distortion, considered in professional circles as the original sin of semi-conductor amplifiers.
With regard to the problem of transmission of electrical signals, the sole object of these investigations, this amplifier can be reduced to the diagram of FIG. 1h. The 1000xcexa9 circuit, adjustable capacitance from 5 to 100 pF, allows the operation of the operational amplifier AOP to be stabilized. This circuit is not essential because the operational amplifier AOP, with a gain of 9.2, is intrinsically stable for this value of gain, but has been added because of the saturation effects in the amplifiers. Indeed, on a musical transient, the saturation, i.e. the limiting transient peak, does not matter to the audience. But this saturation is likely to disrupt the amplifier internal circuit, this latter being then incapable, because of xe2x80x9cindiscriminationxe2x80x9d, of processing correctly the possibly weak signals which can follow this disruption. The adjustment of the value of C is carried out experimentally.
At the time of a first test, during these investigations, the value accepted by M. JOHANNET was 47 pF, the capacitor used being a fixed polystyrene capacitor. The subjective results to the listener were good, any feeling of high level peak limiting having disappeared, but the sound appeared, to the senses of the well-informed audiophiles, xe2x80x9clifelessxe2x80x9d, i.e. without finish.
A second test was then carried out by means of an adjustable TEFLON capacitor, marketed by the PHILIPS Company. This test appeared justified, insofar as such a professional quality capacitor using a dielectric material of the first order, TEFLON, was bound, by means of careful adjustment, to give superior results.
Against all expectation, the sound from the amplifier thus equipped is clearly degraded with an obvious degradation of the tonal quality, a sensation of mixing of the sounds, tending to a disappointing result.
A third counter check test was then carried out, this test consisting in replacing the adjustable TEFLON capacitor with an adjustable air capacitor, without insulation between electrodes. The effect was immediate with disappearance of the degradation of the tonal quality of the amplifier. An adjustment of this new capacitor to a value of the order of 30 pF enabled the regaining of, not only the excellent sound of the original amplifier to be regained, but also of an out of the ordinary capacity of this latter to withstand the signal limiting peaks as well as the subjective impression of a signal transmitted and amplified by an amplifier with a power at least equal to an effective 20 to 30 W.
The disastrous subjective tonal behavior of an electrical circuit or conductor, with on the face of it a capacitance of negligible value, 30 pF, and yet equipped with one of the better dielectric insulators currently used, cannot in any case be attributed to one of the phenomena mentioned previously in the description.
These investigations then led M. JOHANNET to attribute the unsatisfactory behavior of the insulation/conductor interface of the electrical circuits, such as particularly the capacitors, to the existence of dipolar molecules, adsorbed oxygen, at this insulation/conductor interface, as well as electrical micro-discharges at the conductor-insulating molecules interface likely to cause interference radiation generating radio interferences. Justification of such a discovery will be given later in the description.
The object of the present invention is a manufacturing process of a conductor or electrical circuit compensated for radio interferences caused particularly by electrical micro-discharges, of which the surface of this electrical conductor or this circuit or more generally the conductor-insulation interface is inevitably the seat.
Another object of the present invention is to use an electrical conductor or circuit compensated for radio interferences caused particularly by electrical micro-discharges present on the surface of this electrical conductor or this circuit, such micro-discharges on these compensated conductors or circuits being markedly attenuated or eliminated.
Another object of the present invention is to use conductors or electrical circuits likely to be used for the transmission and/or the processing of analogue or digital signals in technical fields as varied as domestic electrical or electronic equipment, HiFi and instrumentation and metrology equipment.
The manufacturing process of an electrical conductor or of a circuit compensated for radio interferences generated particularly by electrical micro-discharge phenomena present on this electrical conductor or this circuit under voltage, the object of the present invention, is remarkable in that it consists in making, on the external bare or insulation coated surface of this conductor or this circuit, an application of a semi-conductor coating material, this semi-conductor material having a resisitivity coefficient value allowing at the same time the external surface of the electrical conductor or circuit to maintain a constant local static value, close to that of the conductor, and to absorb all the random electrical discharge currents caused by these interference phenomena.
The process and the electrical circuit, the objects of the invention, find application not only in the field of HiFi electronic equipment construction but also in home automation, in instrumentation, metrology and the transmission of digital signals.